Re: General-purpose function for sorting data frame

["Jean V Adams" <jvadams@usgs.gov>]

Isn't using rev() a more convenient approach?

In your example:
Oats[order(rev(Oats$nitro), Oats$Variety), ]

For Thom Burnett's recently posted example:
attach(unsortedData)
sortedData <- unsortedData[order(sex, rev(race), rev(smoking), weight), ]
detach("unsortedData")

JVA

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Jean V. Adams
Statistician
U.S. Geological Survey
Great Lakes Science Center
c/o Marquette Biological Station
1924 Industrial Parkway
Marquette, MI 49855  USA
phone: 906-226-1212
FAX: 906-226-3632
web site: www.glsc.usgs.gov
e-mail: jvadams@usgs.gov


                                                                                
                                                         
                      Kevin Wright                                              
                                                         
                      <kwright@eskimo.com>             To:       
s-news@lists.biostat.wustl.edu                                          
                      Sent by:                         cc:                      
                                                         
                      s-news-owner@lists.biosta        Subject:  [S] 
General-purpose function for sorting data frame                     
                      t.wustl.edu                                               
                                                         
                                                                                
                                                         
                                                                                
                                                         
                      09/29/2004 10:04 AM                                       
                                                         
                                                                                
                                                         
                                                                                
                                                         


One of the often asked questions on s-news and r-help relates to sorting
a data frame in ascending/descending order by multiple columns.

I have created a function that does the job very flexibly and in a way that
should be easy to remember.  For example, to sort the Oats data.frame (nlme
library) by nitro (decreasing) and Variety (increasing) :

sort.data.frame(Oats, ~ -nitro + Variety)

Feedback and improvements are welcome.

sort.data.frame <- function(form,dat){  # Author: Kevin Wright
  # Some ideas from Andy Liaw
  #   http://tolstoy.newcastle.edu.au/R/help/04/07/1076.html

  # Use + for ascending, - for decending.
  # Sorting is left to right in the formula

  # Useage is either of the following:
  # library(nlme); data(Oats)
  # sort.data.frame(~-Variety+Block,Oats) # Note: levels(Oats$Block)
  # sort.data.frame(Oats,~nitro-Variety)

  # If dat is the formula, then switch form and dat
  if(inherits(dat,"formula")){    f=dat
    dat=form
    form=f
  }
  if(form[[1]] != "~")
    stop("Formula must be one-sided.")

  # Make the formula into character and remove spaces
  formc <- as.character(form[2])
  formc <- gsub(" ","",formc)
  # If the first character is not + or -, add +
  if(!is.element(substring(formc,1,1),c("+","-")))
    formc <- paste("+",formc,sep="")

  # Extract the variables from the formula
  if(exists("is.R") && is.R()){    vars <- unlist(strsplit(formc,
"[\\+\\-]"))
  }
  else{    vars <- unlist(lapply(unpaste(formc,"-"),unpaste,"+"))
  }
  vars <- vars[vars!=""] # Remove spurious "" terms

  # Build a list of arguments to pass to "order" function
  calllist <- list()
  pos=1 # Position of + or -
  for(i in 1:length(vars)){    varsign <- substring(formc,pos,pos)
    pos <- pos+1+nchar(vars[i])
    if(is.factor(dat[,vars[i]])){      if(varsign=="-")
        calllist[[i]] <- -rank(dat[,vars[i]])
      else
        calllist[[i]] <- rank(dat[,vars[i]])
    }
    else {
      if(varsign=="-")
        calllist[[i]] <- -dat[,vars[i]]
      else
        calllist[[i]] <- dat[,vars[i]]
    }
  }
  dat[do.call("order",calllist),]

}